Never get jealous when you see your ex with someone else, because our parents taught us to give our used toys to the less fortunate. Yup, i need to remember that. Don't worry Katie, you'll find out soon enough that you are the less fortunate now.
Don't her all depressed over a guy (or a girl) from your past. That's like being sad because the garbage man picked up the trash. ---Not saying they are/were trash, but saying it is over, do not dwell.